1. Field of the Invention
The present invention relates to a power up detecting system, and particularly relates to a power up detecting system having more than one trip points.
2. Description of the Prior Art
DRAM devices may have problems such as devices outputs logic values 0 or 1 when not intended during power supply ramp if the power up detecting circuit's trip point is set too low. The power up detecting circuit is utilized to detect the voltage value of the power provided by a power supplier, to generate a power up detecting signal PD. The trip point means the point that the power up detecting signal PD transits from a logic value 0 to a logic value 1 due to that the voltage value of the power up detecting signal PD reaches a predetermined voltage value Vpre, as shown FIG. 1.
Accordingly, if the trip point is set too low, logics of the circuitry may not correctly operate before the power up detecting signal PD trips. However, devices which run on an supply voltage than it ideally would, because the device must be able to function at much lower voltages in order to be tested for low voltage margin.